This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The principal aim of this proposal is to test the hypothesis that individuals with chronic low back pain (LBP) have altered soft tissue biomechanical behavior during acupuncture needling in the lower back and legs compared with individuals without LBP (No-LBP). We will also test whether or not altered tissue behavior in LBP is generalized, or localized to specific locations as predicted by traditional acupuncture theory. This proposal constitutes the first step to testing the mechanistic model that 1) altered soft tissue biomechanical behavior during needling in LBP is due to abnormalities of connective tissue (subcutaneous, perimuscular and/or intramuscular), 2) connective tissue plays an important role in both the therapeutic mechanism of acupuncture and the pathophysiological mechanism of LBP, and 3) these two mechanisms are related. Acupuncturists describe qualitatively different needling responses at locations believed to be "involved" in the patient's disease process. Although assessing abnormalities in the needling response is a fundamental aspect of acupuncture therapy, what constitutes a normal vs. abnormal needling response has never been studied quantitatively. Thus the nature of tissue changes underlying these phenomena remains unknown. We have recently developed a new in vivo technique based on ultrasound elastography in humans that allows visualization and quantification of tissue displacement and strain patterns developed in tissues during needle manipulation (65). In this proposal, we will use ultrasound elastography to perform measurement and detailed analysis of tissue biomechanical behavior during needling in human subjects with and without LBP. AIM 1: Examine tissue biomechanical behavior during acupuncture in LBP vs. No-LBP: 80 subjects with LBP and 80 control subjects without LBP will be tested. We will test acupuncture points (APs) and non-acupuncture points (Non-APs) on the Bladder (BL) and Gall Bladder (GB) meridians as well as Non-Meridian Non-APs in the back and leg. Primary outcome measures will be: 1) peak torque during needle rotation (Torque);2) needle force decay rate during needle oscillation (Force decay);3) tissue displacement (Displacement) in Subcutaneous, Perimuscular and Muscle zones during needle oscillation;4) Perimuscular zone thickness (Thickness). Our preliminary data suggest that tissue behavior during needling in the lower back is abnormal in LBP. We hypothesize that Torque and Displacement are smaller and that Force decay and Thickness are greater 1) in LBP than in No-LBP, 2) at Meridians than at Non-Meridians, 3) at APs than at Non-APs, 4) in the back than in the leg. In LBP subjects, we will also examine the relationship between these outcome measures and 1) subjective pain pattern, 2) tenderness to palpation. AIM 2: Quantify tissue material properties responsible for biomechanical behavior observed in Aim 1: Data from Aim 1 will be used to develop, evaluate and implement a biomechanical model to quantify parameters including stiffness, damping and needle/tissue coupling time constant associated with each of three tissue zones (Subcutaneous, Perimuscular and Muscle). We hypothesize that stiffness is greater and that damping and needle/tissue coupling constant are smaller in LBP compared with No-LBP. These parameters also will be used to generate further hypotheses regarding connective tissue pathophysiological mechanisms potentially responsible for abnormal soft tissue behavior in LBP (e.g. increased or decreased tissue water content, abnormal connective tissue matrix architecture, increased or decreased collagen deposition). These hypotheses will be tested in future studies that will combine ultrasound elastography and tissue biopsies in LBP and No-LBP. AIM 3: Examine the relationship between tissue behavior during acupuncture and clinical assessment prior to needling: In all subjects tested in Aim 1, we will perform clinical measures of muscle length in areas that will be needled as well as range of motion (ROM) and functional assessments. These measurements will be compared with parameters calculated in Aim 2. We hypothesize that stiffness will be negatively correlated, and that damping and tissue coupling constants will be positively correlated with muscle length and ROM in corresponding muscle groups as well as physical performance measures. These data will pave the way for a future clinical trial comparing the effects of acupuncture and physical therapy using both subjective (pain reduction, functional assessment) and objective outcome measures (ultrasound elastography, bulk passive tissue stiffness, kinematic motion analysis and muscle activity) both before and after a series of treatments. This multidisciplinary study bridging the fields of alternative medicine, physical therapy, engineering, physics and orthopaedics will provide objective biomechanical measurements of phenomena fundamental to acupuncture. This study also may 1) lead to important new insights on the pathophysiology of LBP and 2) provide objective biological outcome measures for future clinical trials of acupuncture and other "alternative" manual therapies as well as physical and rehabilitation therapy.